The invention relates to a fuel injector, in particular common rail injector, with a valve housing which can be inserted into a receiving opening of a cylinder head of an internal combustion engine and, in the installed position, has a first valve housing portion facing a combustion chamber of the internal combustion engine, wherein the first valve housing portion is composed of metal and, on the side facing the combustion chamber, is surrounded radially by a sealing element which can be inserted into the annular space between the first valve housing portion and the receiving opening in the region of a first receiving bore portion.
Such a fuel injector which is known in practice serves for injecting fuel into the combustion chamber of an internal combustion engine. For this purpose, the internal combustion engine has, in the region of a cylinder head bounding the combustion chamber, a receptacle in the form of a stepped bore, into which the fuel injector is inserted by the valve housing thereof. The fuel injector projects here with at least one nozzle opening into the combustion chamber of the internal combustion engine. In order to seal the combustion chamber or the cylinder head to the outside, the injector housing of the fuel injector is customarily accommodated in the receiving bore of the cylinder head with the interposition of a nozzle sealing disk and with axial prestress. During the operation of the internal combustion engine, the combustion chamber has the highest temperature, the temperature gradually decreasing in the cylinder head or in the receiving bore on the side facing away from the combustion chamber, depending on the distance from the combustion chamber. In an analogous manner, the temperature of the fuel injector or of the valve housing thereof likewise decreases at an increasing distance from the combustion chamber. In particular in the case of relatively low combustion chamber temperatures or at a relatively large distance from the combustion chamber, the formation of condensate on the valve housing of the fuel injector may occur, inter alia assisted, for example, by sulfurous fuel or by water arising during the combustion of the fuel. Since the valve housing in the cylinder head is sealed toward the outside via the nozzle sealing disk, especially the region axially just below the nozzle sealing disk in the region of a first receiving bore portion of the cylinder head is affected by this since, as seen relatively, the lowest temperatures prevail there. The formation of condensate may result in corrosion of the valve housing occurring in the region discussed, the corrosion, as considered over the service life of the fuel injector, possibly leading to an impairment of the operability of the fuel injector.
In the case of the fuel injector which is known in practice and is used in spark-ignition internal combustion engines (gasoline engines), it is therefore known to provide a sealing element which is composed of plastic and which radially surrounds the valve housing on the side facing the combustion chamber close to the combustion chamber such that the penetration of the condensate in the direction of that side of the fuel injector which faces away from the combustion chamber is at least made difficult. The known sealing element is inserted in a radially encircling annular groove of the valve housing. On transfer to a compression-ignition internal combustion engine (diesel engine), such a solution is not expediently possible since the higher pressures prevailing in the fuel injector (in comparison to the pressures in an injector for a spark-ignition internal combustion engine) cause a weakening of the valve housing by the annular groove, which would lead to a functional impairment, As an alternative thereto, the valve housing would have to have a greater wall thickness, which, for a wide variety of reasons, is neither desirable nor possible in practice since, for example, the diameter of the receiving bore for the fuel injector is predetermined in the region of the valve housing.
Furthermore, DE 101 25 943 A1 discloses a fuel valve for internal combustion engines, in which the valve housing portion facing the combustion chamber is surrounded by a sleeve. However, the sleeve known from the document mentioned serves solely and only for increasing the strength of the valve housing.